Back in the early 2000s ADOT started to hear from drivers who said certain stretches of Valley freeways seemed quieter than others.
ADOT and the Maricopa Association of Governments (MAG) noticed a difference, too.
It seemed that areas paved with an asphalt rubber friction course (rubberized asphalt), which MAG funded through the Regional Transportation Plan, were less noisy than freeway surfaces with cement concrete pavement.